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TypeScript 元数据操作 API 及示例

news 2025/7/4 12:30:39

TypeScript 元数据操作 API 及示例

1. 配置环境

安装依赖

npm install reflect-metadata

tsconfig.json 配置

{
  "compilerOptions": {
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "target": "ES6"
  }
}

2. 元数据操作 API

Reflect.defineMetadata(key, value, target, propertyKey?)
Reflect.getMetadata(key, target, propertyKey?)
Reflect.hasMetadata(key, target, propertyKey?)
Reflect.getMetadataKeys(target, propertyKey?)

3. 内置元数据键

design:type：属性/方法的类型
design:paramtypes：方法参数的类型
design:returntype：方法返回值类型

4. 示例代码

示例 1：自定义装饰器

import "reflect-metadata";

function LogInfo(message: string) {
  return function (target: any, propertyKey: string, descriptor: PropertyDescriptor) {
    Reflect.defineMetadata("log-message", message, target, propertyKey);
  };
}

class UserService {
  @LogInfo("Fetching user data")
  getUser(id: number) {
    return { id, name: "Alice" };
  }
}

const message = Reflect.getMetadata("log-message", UserService.prototype, "getUser");
console.log(message); // 输出: "Fetching user data"

示例 2：内置元数据推断

import "reflect-metadata";

class Example {
  @Reflect.metadata("custom-prop", true)
  public name: string = "";

  greet(@Reflect.metadata("required", true) name: string): string {
    return `Hello, ${name}`;
  }
}

const propType = Reflect.getMetadata("design:type", Example.prototype, "name");
console.log(propType); // 输出: [Function: String]

const paramTypes = Reflect.getMetadata("design:paramtypes", Example.prototype, "greet");
console.log(paramTypes); // 输出: [ [Function: String] ]

示例 3：类级别元数据

import "reflect-metadata";

@Reflect.metadata("api-version", "1.0.0")
class ApiController {
  @Reflect.metadata("http-method", "GET")
  public fetchData() {}
}

const apiVersion = Reflect.getMetadata("api-version", ApiController);
console.log(apiVersion); // 输出: "1.0.0"

const httpMethod = Reflect.getMetadata("http-method", ApiController.prototype, "fetchData");
console.log(httpMethod); // 输出: "GET"